The GNOME project is proud to present GNOME 3.10. The release comes six months after 3.8, and contains 34786 changes by approximately 985 contributors. It contains major new features as well as a large collection of smaller enhancements. 3.10 provides an improved experience for users, as well as new capabilities for application developers.
Since 3.10, many applications have switched to use header bars rather than the traditional combination of titlebar, toolbar and menu bar. This has the advantage of reducing the amount of screen space used by window chrome, keeps the window close button available, and allows dynamic controls that change according to the view in the window.
HeaderBar will replace titlebar from window manager, and user doesn't have option of disabling that. So it's mandatory, but good for smaller applications where you can add all menu items to one drop-down MenuButton. Now GNOME applications, like Evince, will have different window decorations in Openbox than other apps.